Emergency lighting system

Abstract

A lighting system for supplying AC power normally, and DC power on an emergency basis selectively, to electron discharge devices, particularly fluorescent lamps; thus, the AC or DC power is furnished over common lines to a high frequency inverter associated with each lamp or lamp fixture; the arrangement is such that substantially no extra wire or wiring is required for the emergency lighting, whether the installation be a new one or retrofitted. In the latter case, new style electronic ballasts replace the old or core type ballasts in those fixtures that are to provide the emergency lighting; such electronic ballasts including the aforesaid inverter capabilities.

I claim: 
     
       1. An emergency lighting system in which selected ones of the lighting fixtures used for providing normal illumination from an AC utility power supply available at their inputs, can likewise be used to furnish illumination from an emergency DC power supply available at the same inputs, said DC power supply being operatively connected to said lighting fixtures under emergency conditions when said AC utility power supply is discontinued, comprising: a plurality of branch circuits, each having a plurality of lighting fixtures connected therein;   an AC utility power supply normally connected by said branch circuits to said inputs on said lighting fixtures;   a selected branch circuit being provided with emergency lighting fixtures, each of said emergency lighting fixtures comprising an electron discharge lighting device, a high frequency inverter power supply, and a rectifier;   each inverter power supply and each rectifier having an input and an output; the input of said rectifier being continuously connected to said selected branch circuit; the output of said rectifier being continuously connected to the input of said inverter power supply; the output of said inverter power supply being continuously connected to a respective electron discharge lighting device for supplying high frequency power to said lighting device irrespective of whether or not said AC utility power supply is discontinued;   an emergency DC power supply; and,   transfer means responsive to discontinuance of said AC utility power supply for selectively illuminating said emergency lighting fixtures, including switching means for connecting said selected branch circuit to said emergency DC power supply.   
     
     
       2. A lighting system as defined in claim 1, in which all of said emergency lighting fixtures are connected in said selected branch circuit. 
     
     
       3. A lighting system as defined in claim 1, in which said emergency DC power supply is a battery centrally located remote from said lighting fixtures. 
     
     
       4. A lighting system as defined in claim 3, in which said emergency DC power supply further includes a charging device for continuously supplying an appropriate DC charging current to said battery, except when said AC supply is discontinued. 
     
     
       5. A lighting system as defined in claim 1, in which said switching means for connecting said selected branch circuit to said emergency DC power supply includes a relay coil connected to said AC utility power supply and normally closed relay contacts connected to said selected branch circuit.